Gas fluxes of N2O, NO and NH3 to the atmosphere
The acceleration of the global nitrogen (N) cycle due to human activities is the major cause of the increase in the atmospheric nitrous oxide (N2O) concentration of 0.7 ppb per year and of the increasing emissionof nitric oxide (NO) into the atmosphere.
Human activities and the increase in the atmospheric nitrous oxide (N2O) concentration
Nitrous oxide is one of the so-called greenhouse gases, constituting 6% of the anthropogenic greenhouse effect, and also contributing to the depletion of stratospheric ozone. Although the individual sources of N2O are poorly known, the use of N fertilizers and animal manure are recognised as the main anthropogenic sources responsible for the atmospheric increase (Houghton et al., 2001). Nitric oxide participates in the regulation of the oxidant balance of the atmosphere. In the atmosphere NO is oxidised to NO2. Redeposition of NOx (NO and NO2 being collectively denoted as NOx) contributes to acidification and eutrophication of ecosystems. Agricultural fields are not major sources of NO worldwide. However, being the dominant source in regions away from fossil fuel combustion sources, agricultural NO emissions play an important role in local tropospheric ozone chemistry.
PBL studies on the subject
An early widely cited paper (>150 citations) paper used measurement data to estimate fertiliser-induced N2O emissions from agricultural fields (Bouwman, 1996).This paper formed the basis for the IPCC default emission factor used in the guidelines for national inventories of greenhouse gas emissions (IPCC, 1997). Three more recent PBL studies focus on N2O and NO emissions from agricultural systems. In 2002, PBL (at that time the RIVM) published two articles (Bouwman et al., 2002c; Bouwman et al., 2002a) based on information taken from 846 N2O emission measurements in agricultural fields; 99 measurements for NO emissions was summarised to assess the influence of various factors regulating emissions from mineral soils. In 2006 an update of these studies based on more measurement data and extended with data for natural ecosystems was published by PBL (Stehfest and Bouwman, 2006). The results of this study were used to update the default emission factor for N2O in the update of the IPCC guidelines (IPCC, 2006). In 2007 a paper was published on the potential sink strength at the earth’s land surface (Kroeze et al., 2007).
N deposition and NH3
Atmospheric N deposition rates on the earth’s surface have increased from 3-fold to more than 10-fold since pre-industrial times. In terrestrial ecosystems eutrophication due to increased N deposition has a number of important negative impacts, including loss of biodiversity. Apart from NOx, the major source of the re-deposited reactive nitrogen is ammonia (NH3). In the atmosphere NH3 neutralises a large portion of the acids produced by oxides of sulfur and nitrogen. Most of the atmospheric aerosols, acting as cloud condensation nuclei, consist of sulfate, neutralised to various extents by NH3. Most of the NH3 is returned to the surface by deposition, which is known to be one of the causes of soil acidification. The role of NH3 as a fertiliser was already known more than a century ago. In the last few years there has been growing concern about the eutrophication of natural ecosystems and loss of biodiversity due to N deposition.
In 1997 PBL (at that time RIVM) published a global inventory of NH3 emissions in a widely cited article (>150 citations) (Bouwman et al., 1997). Part of this inventory - the NH3 emissions from fertiliser and animal-manure N application in agricultural systems- has been updated recently (Bouwman et al., 2002b); it will be followed by an uncertainty analysis (Bouwman et al., 2006a). The different components of the NH3 emission inventory have now been incorporated into the IMAGE framework (PBL, at that time MNP, edited by Bouwman, 2006). The above PBL (at that time MNP) studies on emissions of N2O, NO and NH3 were summarised and presented at the Third Nitrogen Conference, Nanjing, China (Bouwman et al., 2005d).
Further work on this topic at PBL involved an analysis of the effects of re-deposited N and SO2 (Bouwman and Van Vuuren, 1999; Bouwman et al., 2002d).
References
- cited PBL references
- IPCC (2006) IPCC Guidelines for National Greenhouse Gas Inventories, IPCC NGGIP Programme, IPCC-TSU/IGES. Published by the Institute for Global Environmental Strategies (IGES), Hayama, Japan for the IPCC, Hayama, Japan.
